Visualization and Quantitation of Phase-Separated Droplet Formation by Human HP1α.

The ability of the heterochromatin protein-1 (HP1) to phase separate into droplets suggests new mechanisms of gene organization in the cell nucleus. An accumulating body of work suggests that other nuclear proteins also display phase separation behaviors in vitro. To understand the mechanistic and biological significance of such droplet formation a rigorous biophysical characterization of this behavior is necessary. Herein we describe procedures for imaging HP1 droplets by brightfield microscopy, and two methods to quantify phase separation.